Temporary partial breakdown of Mlo-resistance in spring barley by the sudden relief of soil water stress

Seedlings of spring barley cultivars expressing mlo genes for resistance to mildew (Erysiphe graminis f.sp. hordei) in different genetic backgrounds were subjected to degrees of water stress under different nutrient and soil conditions. The temporary breakdown in the host of the expression of Mlo-resistance, reported occasionally under field conditions, was successfully simulated when stress treatments were relieved. Differences in the degree of temporary breakdown were attributable to nutrient status, soil compaction and genetic background of the mlo gene.     

Relationships between populations of Pseudomonas syringae pv. persicae determined by restriction fragment analysis

Pseudomonas syringae pv. persicae , the pathogen causing bacterial decline of stone-fruit, was first noted almost simultaneously in France and in New Zealand, together with a closely related pathogen from myrobalan plum in England. The relative similarity of 31 strains from these three countries was examined by comparing DNA restriction endonuclease fragment patterns. Fragment patterns produced from digested DNA samples which were electrophoresed on polyacrylamide gels and visualized by silver-staining, were analysed using the software package Gelcompar. The fragment patterns produced by strains from France and England formed homogeneous but separate groups, while those from New Zealand were relatively heterogeneous. This finding suggests that the New Zealand population of P.s. persicae is older than those found in Europe. Problems in explaining the distribution of the pathogen are discussed.     

Evidence of density-dependent effects on population variation of Japanese sardine (Sardinops melanosticta) off Korea

Interannual variation of some biological parameters for the Japanese sardine, Sardinops melanosticta, population in Korean waters was investigated using scientific surveys and fisheries information since the late 1970s. The abundance and geographical coverage of sardine eggs were high (peak in 1986) and broad when spawning biomasses were high in the mid 1980s, and vice versa in the late 1970s and the early 1990s. Also, feeding and spawning areas based on fisheries information exhibited the same pattern of expansion/contraction as seen in ichthyoplankton surveys. Annual Gonadal Somatic Index (GSI) in spawning season (February to April) and the size at age 1 of sardine were reduced during the high abundance period. It is suggested that density‐dependent effects on the reproduction and growth of the sardine population in Korean waters existed.     

The effect of antibody to caseous lymphadenitis in ewes on the efficacy of vaccination in lambs

The effect of maternal antibody to the toxin of Corynebacterium pseudotuberculosis, produced by caseous lymphadenitis (CLA) in ewes or by vaccinating ewes before lambing, on the efficacy of vaccination against CLA in their lambs was examined. Lambs were allocated to treatments according to either the vaccination history of their dam or level of CLA toxin antibody of their dam. They were vaccinated twice using 2 different inoculation regimes and then artificially infected with CLA organisms. The number of lambs with CLA lesions was assessed at slaughter. In one experiment high levels of CLA toxin antibody activity in ewes were associated with decreased efficacy of CLA vaccination in their lambs, when lambs were vaccinated at 2 and 8 weeks or 8 and 14 weeks of age. In a second experiment the efficacy of lamb vaccination at 8 and 12 weeks, but not at 14 and 18 weeks of age, was decreased. In sheep flocks with a high prevalence of CLA, vaccinating lambs against CLA at less than 10 weeks of age may not produce optimum protection against CLA in lambs. There was no difference in infection rate between lambs from vaccinated and unvaccinated ewes. However, vaccination of lambs at 2 and 8 wks was less effective that vaccination at 8 and 14 weeks, probably due to reduced immunocompetence in young lambs. In sheep flocks where significant numbers of lambs receive their primary vaccination at less than 3 weeks of age vaccination programmes to control CLA in lambs may be less effective.